How to use it
- Pick your flooring and layout. The layout fills in a typical waste factor, and you can change it.
- Enter the room length and width in feet, plus inches if you have them, or switch Units to metric. Turn on a second area for a closet, a hall or the other half of an L-shaped room.
- Type the square feet per box from the carton or product page.
- Turn on the extras you need: underlayment, thinset and grout for tile, or baseboard and quarter round.
- Type prices in the cost section to see a total.
Results update as you type. Copy result gives you a plain-text list for the store, and the page address saves your numbers so you can come back to them.
Measuring a room that isn't a rectangle
Sketch the floor and split it into rectangles. An L-shaped room is two: measure each one and add them. Measure wall to wall, not baseboard to baseboard, and round up to the next inch. Don't subtract for a vanity or island unless the floor stops at it, and don't skip small bump-outs and closets.
The formula
Floor area = Length × Width (+ second area)
Area with waste = Floor area × (1 + Waste % ÷ 100)
Boxes = Area with waste ÷ Sq ft per box, rounded up
Underlayment rolls = Floor area ÷ Sq ft per roll, rounded up
Thinset bags = Floor area ÷ Coverage per bag, rounded up
Grout lb per sq ft = (L + W) ÷ (L × W) × Joint × Thickness × Grout lb per cu ft ÷ 12
Trim pieces = (Walls − Openings) × (1 + Trim waste % ÷ 100) ÷ Piece length, rounded up
The grout line is the joint-volume formula grout makers print on their product data sheets, converted to inches and pounds. L and W are the tile size in inches, and the joint depth is taken as the tile thickness. The waste factor covers cut pieces, so it goes on the flooring only. Thinset, grout and underlayment are figured on the floor itself.
Worked example: a 12 × 14 ft bedroom with a 3 × 5 ft closet
- Floor area: 168 + 15 = 183 sq ft
- Straight lay with 10% waste: 183 × 1.10 = 201.30 sq ft
- Boxes at 20 sq ft: 201.3 ÷ 20 = 10.07, so 11 boxes (220 sq ft)
- Underlayment: 183 ÷ 100 = 1.83, so 2 rolls
- Baseboard: walls are 52 + 16 = 68 ft. Openings are a 3 ft entry door plus the 2.5 ft closet door counted twice, 8 ft in all. 68 − 8 = 60 ft, plus 10% = 66 ft, so 9 pieces of 8 ft
- In 12 × 24 tile with 1/8 in joints, 3/8 in thick: 0.0488 lb of grout per sq ft × 183 = 8.94 lb, so 1 bag of 25 lb. Thinset at 60 sq ft per bag: 183 ÷ 60 = 3.05, so 4 bags
Why buy extra, and keep a spare box
Every row ends in a cut, and diagonal and herringbone layouts cut at angles along every wall, which is why they need more. The bigger reason to buy extra comes later: styles get discontinued, and a new run rarely matches. One spare box means a damaged plank or cracked tile is a small repair instead of a new floor.
Buy it all at once and check the lot or dye batch number on every carton (tile also has shade and caliber codes). Pull from several boxes as you go so small differences blend.
Acclimation and expansion gaps
Wood and laminate move with humidity, so most makers want the boxes to sit in the room before you install. Floating floors need a gap at every wall, which the baseboard or quarter round covers. The instructions in the box give the time and the gap, and the warranty usually depends on them.
Common mistakes
- Forgetting closets and halls. They're easy to leave off and they add up.
- Using the wrong box coverage. Two products that look alike can cover very different square footage per carton.
- Buying short and going back later. The next lot may not match.
- Skipping the prep. Most floors need a flat, clean subfloor. Leveling compound and transitions are extra.
Questions people ask
How much extra flooring should I buy?
Common guidance is about 5 to 10% for a straight lay, about 15% for diagonal and 15 to 20% or more for herringbone. Rooms with lots of corners need more. The calculator starts at the top of each range, and the product's instructions may suggest a different number.
Do I need underlayment?
Some vinyl and laminate has a pad attached, and the maker may say not to add another. Concrete subfloors often call for a moisture barrier. Follow your product's installation guide.
How is the grout amount figured?
It's the volume of the joints, from the tile size, joint width and depth, turned into pounds. Big tile with narrow joints uses very little; small tile with wide joints uses much more. If your bag lists coverage for your tile, use that.
How do I price installation?
Installers often quote per square foot. Ask whether they figure it on the room or on the material, multiply, and enter the total as labor. Removing old flooring and fixing the subfloor are often priced separately.